In recent years, attention has been focused on solar energy as an energy source because of environmental problems and so forth.
Methods of converting light or heat of solar energy into electrical energy as usable energy have been practically available.
Among these methods, a method of converting sunlight into electrical energy, for example, is a typical example, and a photoelectric conversion element is utilized in this method.
The photoelectric conversion element in which an inorganic material such as single crystalline silicon, polycrystalline silicon, amorphous silicon, and cadmium telluride, indium copper selenide or the like is employed is widely used as a photoelectric conversion element, and has been utilized for a so-called solar cell.
A solar cell fitted with a photoelectric conversion element in which the inorganic material is used had problems such as complicated manufacturing processes together with a number of processes at high production cost and so forth because of a multilayer p-n junction structure in which a high purity product obtained via a high purification process for silicon used as a material or the like is demanded.
On the other hand, studies of a photoelectric conversion element in which an organic material is used as a simple element have been also in progress.
As described in C. W. Jang: Applied Physics Letters, 48, 1.83 (1986), for example, reported is a p-n junction type organic photoelectric conversion element in which a perylenetetracarboxylic acid derivative as a n-type organic dye and a copper phthalocyanine as a p-type organic dye are joined.
In order to improve a short exciton diffusion length and thin thickness of a space-charge layer taken into account as a drawback, results thereof are being made by largely increasing the area of a p-n junction region where organic thin films are simply layered, and by sufficiently trying to secure the number of organic dyes involved in charge separation.
Further, as described in G. Yu, J. Gao, J. C. Humelen, F. Wudl and A. J. Heeger: Science, 270, 1789 (1996), disclosed is a technique by which the p-n junction region is largely increased by mixing a n-type electron-conductive organic material and a p-type hole-conductive polymer in the film to conduct charge separation in the entire film. Propose was a photoelectric conversion element in which Heeger et al. made a conjugated polymer to be a p-type conductive polymer in 1995 to mix fullerene as an electron-conductive material.
Such a photoelectric conversion element gradually exhibits an improved property thereof, but stable behavior with high conversion efficiency has not been obtained yet.
However, in 1991, Gratzel succeeded in preparation of a photoelectric conversion element having a high conversion efficiency in stable operation by preparing porous titanium oxide, and sufficiently securing the charge separation area (the number of molecules contributed for charge separation) in detailed experiments having been enormously compiled.
In the case of this photoelectric conversion element, repeated are cycles in which a dye adsorbed onto the surface of porous titanium oxide is optically excited and becomes a dye cation via electron-injection from the dye to the titanium oxide, and the dye receives electrons from the counter electrode via a hole transport layer. An electrolytic solution in which an electrolyte containing iodine is dissolved in an organic solvent is used as a hole transport layer.
This photoelectrical conversion element produces excellent reproducibility together with stability of titanium oxide, and in large expansion of an R&D base, and this photoelectric conversion element is also called a dye-sensitizing type solar cell, whereby large expectation and attention have been received.
This technique shows the advantage of being able to use inexpensive semiconductors since inexpensive metallic compound semiconductors such as titanium oxide and so forth are not necessary to be refined up to high purity, and of effectively converting sunlight having a large amount of the visible light component into electricity since usable light extends up to the broad visible light region.
However, since a ruthenium complex exhibiting resource restriction given to a photoelectric conversion layer, an expensive ruthenium complex should be used, and there appears a problem such as insufficient stability produced during aging.
Further, as another problem, since a dye-sensitizing type solar cell is operated with the foregoing electrolyte solution, there further appears another problem such that a mechanism to avoid retention and outflow dissipation of an electrolyte and iodine should be separately provided.
A lead storage battery and a lithium cell are typified as typical examples of other electrochemical elements each possessing an electrolytic solution, but a secondary problem appears to be clearly induced when dissipated chemical species are newly stored in the environment since no 100% of even the compactly modularized electrochemical element has been collected and the compactly modularized electrochemical element has not always been recycled.
An all-solid-state dye-sensitizing type solar cell further taking over the advantage of a dye-sensitizing type solar cell, for which such electrolytic solution problems are avoided, is now in progress.
In this field, those in which amorphous organic hole transfer agents are employed as described on U. Bach, D. Lupo. P. Comte, J. E. Moser, F. Weissortel, J. Salbeck, H. Spreitzer and M. Gratzel, Nature, 395, 583 (1998), and those in which copper iodide is used for a hole transfer agent as described in G. R. A. Kumara, S. Kaneko, M. Kuya, A. Konno and K. Tennakone: Key Engineering Materials, 119, 228 (2002), but since the hole transfer agent exhibits low conductivity, a sufficient photoelectric conversion efficiency has not yet been given.
Further, as a hole transfer agent exhibiting considerably high conductivity, a polythiophene based material is provided as a typical example, and an all-solid-state dye-sensitizing type solar cell in which PEDOT is used as a hole transport agent is reported (refer to Patent Document 1 and Non-patent Document 2, for example).
Further, a photoelectric conversion element in which polyisothianaphthene is used as a hole transport agent has been reported (Patent Document 2). However, since PEDOT exhibits absorption in the visible light range between 400-700 nm, loss is generated with respect to light absorption of a dye, resulting in insufficiency in photoelectric conversion efficiency. Further, polyisothianaphthene disclosed in Patent Document 2 also has not yet been sufficient in photoelectric conversion function stability.    Patent Document 1: Japanese Patent O.P.I. (Open to Public inspection) Publication No. 2003-317814    Patent Document 2 Japanese Patent O.P.I. Publication No. 2009-40903    Non-patent Document 1: B. O'Regan and M. Gratzel: Nature, 353, 737 (1991)    Non-patent Document 2: J. Xia, N. Masaki, M. Lira-Cantu, Y. Kim, K. Jiang and S. Yanagida: Journal of the American Chemical Society, 130, 1258 (2008).